Subminiature optical system and portable device including the same

ABSTRACT

There are provided a subminiature optical system having a miniature size and capable of obtaining a narrow view angle using only five sheets of lenses, and a portable device having the same. The subminiature optical system includes a first lens convex toward the object side and having positive refractive power a second lens concave toward an image side and having negative refractive power, a third lens convex toward the object side and having positive refractive power, a fourth lens concave toward the image plane and having negative refractive power, and a fifth lens convex toward the image plane and having negative or positive refractive power, sequentially from an object side.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. patent application Ser. No.14/927,682 filed Oct. 30, 2015, which is a Continuation of U.S. patentapplication Ser. No. 13/862,102 filed on Apr. 12, 2013, which claims thebenefit under 35 USC 119(a) of Korean Patent Application No.10-2013-0007047 filed on Jan. 22, 2013, in the Korean IntellectualProperty Office, the entire disclosures of which are incorporated hereinby reference for all purposes.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a subminiature optical system and aportable device including the same, and more particularly, to asubminiature optical system having a subminiature size, capable ofobtaining a narrow view angle using five sheets of lenses and a portabledevice including the same.

Description of the Related Art

Initial portable terminals only included a communications function.However, in accordance with an increase in the usage of portableterminals, various functions such as image capturing and the ability totransmit images via communications networks have been implemented inportable terminals. Therefore, functions of, and services available withregard to portable terminals are constantly evolving. Therefore, digitalcamera technology, camcorder technology, and the like have become basicfunctions of portable terminals such as mobile phones.

Camera and camcorder technologies included in mobile phones requiregeneral camera and camcorder performance, while the miniaturization andlightening of image capturing lenses have been strongly demanded.

Therefore, in order to satisfy the above-mentioned requirement, thenumber of the lens provided as image capturing lenses mounted in mobilephones needs to be decreased by as much as possible. However, it may bedifficult to satisfy the requirements for a desired level of opticalperformance due to a lack of design freedom resulting therefrom.

In addition, wide-angle optical systems able to capture images of 70degrees or more have recently been employed in order to capture imageshaving wider backgrounds. However, the wide-angle optical system issuitable for capturing images having wide backgrounds, but is notsuitable for imaging a subject by zooming in on a distant object.

Therefore, an optical system having a small size and capable of clearlyimaging a subject at a long distance is required.

RELATED ART DOCUMENT

Korean Patent Laid-Open Publication No. 2008-0057738

SUMMARY OF THE INVENTION

An aspect of the present invention provides a subminiature opticalsystem having high resolution and having a compact shape and the shortoverall length due to only five sheets of lenses being used therein, anda portable device including the same.

In addition, an aspect of the present invention provides a subminiatureoptical system having a narrow view angle of 35 degrees or less and aportable device including the same.

According to an aspect of the present invention, there is provided asubminiature optical system, including: sequentially from an objectside, a first lens convex toward the object side and having positiverefractive power; a second lens concave toward an image side and havingnegative refractive power; a third lens convex toward the object sideand having positive refractive power; a fourth lens concave toward theimage plane and having negative refractive power; and a fifth lensconvex toward the image plane and having negative or positive refractivepower.

A focal distance of the optical system may satisfy the followingConditional Equation 1,

0.7<TTL/F<1.0   (Conditional Equation 1)

where TTL indicates a distance from a first surface, an object sidesurface, of an optical lens to the image plane, and F indicates thefocal distance of the optical system.

A view angle of the optical system may satisfy the following ConditionalEquation 2,

20<FOV<35   (Conditional Equation 2)

where FOV indicates the view angle of the optical system.

The first lens of the optical system may satisfy the followingConditional Equation 3,

0.16<rdy s1/F<2   (Conditional Equation 3)

where rdy s1 indicates a radius of curvature of the object side surfaceof the first lens, and F indicates the focal distance of the opticalsystem.

An Abbe number of the fourth lens may satisfy the following ConditionalEquation 4,

Vd4>50   (Conditional Equation 4)

where Vd4 indicates the Abbe number of the fourth lens.

The fourth lens may have both surfaces thereof formed to be concave.

The fifth lens may have at least one inflection point formed in alocation thereof other than a location corresponding to an optical axis.

The subminiature optical system may further include an aperture stopdisposed on the object side of the first lens.

According to an aspect of the present invention, there is provided aportable device, including: a first optical system; and a second opticalsystem having a view angle narrower than that of the first opticalsystem.

The second optical system may have the view angle of 35 degrees or less.

The first optical system may have the view angle of 60 degrees through80 degrees.

The second optical system may include: sequentially from an object side,a first lens convex toward the object side and having positiverefractive power; a second lens concave toward an image side and havingnegative refractive power; a third lens convex toward the object sideand having positive refractive power; a fourth lens concave toward theimage plane and having negative refractive power; and a fifth lensconvex toward the image plane and having negative or positive refractivepower.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a lens configuration diagram showing a lens arrangement of asubminiature optical system according to a first embodiment of thepresent invention;

FIGS. 2 and 3 are graphs showing aberration characteristics of theoptical system shown in FIG. 1;

FIG. 4 is a lens configuration diagram showing a lens arrangement of asubminiature optical system according to a second embodiment of thepresent invention;

FIGS. 5 and 6 are graphs showing aberration characteristics of theoptical system shown in FIG. 4; and

FIG. 7 is a perspective diagram schematically showing a portable deviceaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the inventive concept will be described indetail with reference to the accompanying drawings. The invention may,however, be embodied in many different forms and should not be construedas being limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thoseskilled in the art.

FIG. 1 is a lens configuration diagram showing a subminiature opticalsystem according to a first embodiment of the present invention. In thefollowing lens configuration diagrams, thicknesses, sizes and shapes ofthe lenses depicted therein are slightly exaggerated for descriptivepurposes. Particularly, shapes of semispherical surfaces or asphericalsurfaces suggested in the lens configuration diagram are only examples.Therefore, the lenses of the present invention are not to be construedas being limited to the above-mentioned shapes.

As shown in FIG. 1, a subminiature optical system 100 according to theembodiment of the present invention is configured to include a firstlens L1, a second lens L2, a third lens L3, a fourth lens L4, and afifth lens L5, disposed sequentially from an object side. Therefore,light corresponding to image information of a subject passes through thefirst lens L1, the second lens L2, the third lens L3, the fourth lensL4, and the fifth lens L5 so as to be incident to an image plane IP,that is, light receiving element.

The first lens L1, according to the present embodiment, is convex towardthe object side and has positive refractive power. Here, an aperturestop (AS) adjusting an amount of light may be provided between the firstlens L1 and the object.

The second lens L2 is concave toward an image side and has negativerefractive power.

The third lens L3 is convex toward the object side and has positiverefractive power.

The fourth lens L4 is concave toward the image side and has negativerefractive power.

The fifth lens L5 is convex toward an image side in a paraxial regionwith regard to a central axis of incident light. In this case, bothsurfaces of the fifth lens L5 may be formed as aspherical surfaces.

Meanwhile, an optical filter OF configured of an infrared filter, aglass cover, or the like, is included between the fifth lens L5 and theimage plane IP. In particular, the optical filter OF according to thepresent embodiment may be an IR cut filter. The IR cut filter serves toremove radiant heat from external light so as not to transfer heat tothe image plane. That is, the IR cut filter has a structure in which itallows visible light rays to be transmitted therethrough and reflectsinfrared rays to the outside.

In addition, the image plane IP on which an image is formed may beconfigured of an image sensor converting optical signals correspondingto a subject image into electrical signals. In this case, the imagesensor may be configured of a CCD or CMOS sensor.

The subminiature optical system 100 according to the embodiment of thepresent invention may provide thinness to the optical system 100 andhigh definition resolution by ideally setting a ratio of a distance froman object side surface of the first lens L1 to the image plane to afocal distance of the entire optical system, and a ratio of a radius ofcurvature of an object side surface of the first lens to a focaldistance of the entire optical system.

Here, all surfaces of the first lens L1, the second lens L2, the thirdlens L3, the fourth lens L4, and the fifth lens L5 according to thepresent embodiment may be formed as aspherical surfaces. Therefore, thesubminiature optical system 100 may be implemented to be compact whilebeing configured of five lens sheets and having high resolution. Inaddition, in the case in which all of the first lens L1, the second lensL2, the third lens L3, the fourth lens L4, and the fifth lens L5 areformed of a plastic material, an aspheric lens may be easily andeconomically manufactured.

In addition, the fourth lens L4 according to the present embodiment maybe formed so that an Abbe number thereof exceeds 50.

Further, the subminiature optical system 100 according to the presentembodiment may prevent a phenomenon in which the periphery of the imagesensor becomes dark and image distortion occurs, by reducing an incidentangle of an edge of the lens to allow amounts of light in the centralportion and the periphery of the image sensor to be uniform, and tosecure as high a level of ambient light as possible by appropriatelyforming aspherical surfaces on respective lenses, for example,configuring the first lens L1, the second lens L2, the third lens L3,and the fourth lens L4 to sequentially have positive refractive power,negative refractive power, positive refractive power and negativerefractive power, forming an inflection point on the object side surfaceof the fifth lens L5, and the like.

In particular, the subminiature optical system according to the presentembodiment may include the fourth lens having both surfaces formed to beconcave thereon in order to form the view angle to be relatively narrow(for example, 35 degrees or less). In addition, the object side surfaceof the fifth lens may have the inflection point in a location thereofother than a location corresponding to the optical axis. According tothe structure of the fifth lens as described above, a chief ray angle(CRA) of the fifth lens and the CRA of the image sensor (i.e., the imageplane) are matched, such that an amount of light in the periphery of theimage sensor may be secured.

Meanwhile, in the case in which the fifth lens has no inflection point,matching properties with the image sensor are degraded andthrough-the-lens (TTL) metering may be too long, such that it may bedifficult to implement thinness.

Under the entire configuration as described above, acting effects of thefollowing Conditional Equations 1 through 6 will be described.

0.7<TTL/F<1.0   (Conditional Equation 1)

Where TTL is a distance from a first surface, an object side surface, ofthe optical lens to the image plane, and F is the focal distance of theoptical system.

Conditional Equation 1 is a relationship between TTL and power.Therefrom, the TTL is designed to be significantly shorter than thefocal distance F of the optical system, such that it may be appreciatedthat this is contrasted to a camera module according to the related art.

Here, in the case in which a value of TTL/F is decreased by increasingthe focal distance F, the view angle of the optical system (FOV) may befurther decreased. However, since it is difficult to decrease TTL, theoptical system becomes longer, such that it is difficult to implementthinness.

20<FOV<35   (Conditional Equation 2)

Where, FOV is a view angle of the optical system.

Conditional Equation 2, an equation representing view anglecharacteristics of the optical system, has a ratio about 0.5 timesgreater than the view angle (for example, 60 through 75 degrees) of thesubminiature camera module according to the related art. This mayrepresent zoom characteristics of 2.5 through 3 times in the case ofconverting to a general zoom lens.

0.16<rdy s1/F<2   (Conditional Equation 3)

where rdy s1 is a radius of curvature of an object side surface of thefirst lens, and F is the focal distance of the optical system.

Conditional Equation 3 is an equation representing characteristics forthe radius of curvature of the first lens. A configuration capable ofachieving thinness and a relatively small view angle is defined bydecreasing the curvature of an object side surface of the first lens andincreasing the focal distance.

Vd4>50   (Conditional Equation 4)

Where, Vd4 is an Abbe number of the fourth lens.

Conditional Equation 4 defines material characteristics of the fourthlens. That is, the subminiature optical system according to the presentembodiment has the fourth lens configured to have the Abbe number of 50or more. When the optical system 100 is designed so that the fourth lensL4 satisfies a range of Conditional Equation 4, a chromatic aberrationmay be appropriately corrected.

Hereinafter, the present invention will be described through an exampleof specific numerical values.

The optical systems of the following embodiments 1 and 2 include theaperture stop (AS), the first lens L1, convex toward the object side,the second lens L2, concave toward the image side, the third lens L3,convex toward the object side, the fourth lens L4, concave toward theimage side, and the fifth lens L5, convex toward the image side,sequentially from the object side, as described above. In addition, thefirst lens L1 may have positive refractive power, the second lens L2 mayhave negative refractive power, the third lens L3 may have positiverefractive power, the fourth lens L4 may have negative refractive power,and the fifth lens L5 may have negative or positive refractive power.

In addition, an optical filter (OF) 11 and 12 configured of an infraredfilter, a glass cover, or the like is included between the fifth lens L5and the image plane IP.

The aspherical surface used in the following respective embodiments maybe obtained from known Equation 1.

$\begin{matrix}{Z = {\frac{{cY}^{2}}{1 + \sqrt{1 - {\left( {1 + K} \right)c^{2}Y^{2}}}} + {AY}^{4} + {BY}^{6} + {CY}^{8} + {DY}^{10} + {EY}^{12} + {FY}^{14} + \ldots}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Where, Z indicates a distance from the top of a lens in an optical axisdirection.

Y indicates a distance in a direction vertical to an optical axis.

c indicates a radius of curvature at the top of the lens.

K indicates a Conic constant.

A, B, C, D, and E indicate fourth order, sixth order, eighth order,tenth order, and twelfth order aspherical surface coefficients,respectively.

Meanwhile, an aspherical surface used in the following embodiments isobtained from known Equation 1, and ‘E used in the Conic constant (K)and aspherical surface coefficients (A, B, C, D, and E) and numeralsnext thereto’ indicate powers of 10. For example, E+01 indicates 10¹,and E-02 indicates 10⁻².

Embodiment 1

The following Table 1 shows examples of numerical values according to afirst embodiment of the present invention.

FIG. 1 is the configuration diagram of a lens showing lens dispositionof a subminiature optical system according to the first embodiment ofthe present invention; and FIGS. 2 and 3 show aberration characteristicsof the subminiature optical system shown in Table 1 and FIG. 1.

In the subminiature optical system according to the first embodiment ofthe present invention, F number FNo is 2.8, the view angle is 30degrees, the entire focal distance F is 7 mm, the focal distance F1 ofthe first lens is 3.57 mm, the focal distance F2 of the second lens is−4.18 mm, the focal distance F3 of the third lens is 4.35 mm, the focaldistance F4 of the fourth lens is −2.43 mm, and the focal distance F5 ofthe fifth lens is 14.18 mm.

In addition, the distance TTL from an object side surface of the firstlens to the image plane is 5.8 mm.

TABLE 1 Surface Radius of Thickness or Refractive Number CurvatureDistance Index Abbe Number Note 1* 1.34414 0.843041 1.544 56.0 2*3.35746 0.1 First lens 3* −15.4179 0.3 1.632 23.4 4* 3.25711 0.154324Second lens 5* 1.58574 0.491592 1.544 56.0 6* 4.23635 0.91273 Third lens7* −2.31497 0.2 1.544 56.0 8* 3.23536 0.655748 Fourth lens 9* −6.897881.24256 1.544 56.0 10*  −3.88237 0.1 Fifth lens 11  ∞ 0.3 1.517 64.2Filter 12  ∞ 0.43 13  ∞ 0 Image plane

In table 1, * indicates an aspherical surface, and in the firstembodiment, refracting surfaces of all lenses are aspherical surfaces.

Values of aspherical surface coefficients of the first embodiment byEquation 1 are represented by the following Table 2.

TABLE 2 Surface Aspherical Surface Coefficient Number A B C D E F 1−0.02171 0.048614 −0.11407 0.103264 −0.04102 0 2 −0.06114 0.059542−0.10463 0.066754 −0.01566 0 3 0.030857 0.116819 −0.16033 0.11937−0.02948 0 4 0.029406 0.167422 0.059155 −0.14472 0.321946 0 5 −0.171470.011655 −0.02614 0.182498 −0.1343 0 6 −0.09565 −0.16018 0.098417−0.02775 −0.07438 −0.01875 7 −0.28899 −0.04165 −0.66783 0.793086 1.77385−3.31921 8 −0.04374 −0.22428 0.415129 0.086281 −0.61168 −0.20163 90.036288 0.026006 0.00135 −0.00211 −0.00111 −0.00032 10 −0.110940.003295 0.02016 0.000246 −0.00165 −0.00019

Embodiment 2

The following Table 3 shows examples of numerical values according to asecond embodiment of the present invention.

In addition, FIG. 4 is a configuration diagram of a lens showing lensdisposition of a subminiature optical system 200 according to the secondembodiment of the present invention; while FIGS. 5 and 6 show aberrationcharacteristics of the subminiature optical system shown in Table 3 andFIG. 4.

In the second embodiment of the present invention, F number FNo is 2.8,the view angle is 28 degrees, the entire focal distance F of the opticalsystem is 7.5 mm, the focal distance F1 of the first lens is 3.6 mm, thefocal distance F2 of the second lens is −5.35 mm, the focal distance F3of the third lens is 6.6 mm, the focal distance F4 of the fourth lens is−3.1 mm, and the focal distance F5 of the fifth lens is −16 mm.

In addition, the distance TTL from an object side surface of the firstlens to the image plane is 6 mm.

TABLE 3 Surface Radius of Refractive Abbe Number Curvature ThicknessIndex Number Note 1* 1.38923 0.768867 1.544 56.0 2* 3.81076 0.1 Firstlens 3* −28.1935 0.240438 1.632 23.4 4* 3.9058 0.306891 Second lens 5*2.10006 0.418991 1.544 56.0 6* 4.67386 1.07606 Third lens 7* −3.11130.16 1.544 56.0 8* 3.78175 0.682294 Fourth lens 9* −11.1737 1.083211.544 56.0 10*  50.6176 0.131032 Fifth lens 11  ∞ 0.3 1.517 64.2 Filter12  ∞ 1.18 13  ∞ 0 Image plane

In the table 3, * indicates an aspherical surface, and in the firstembodiment, refracting surfaces of all lenses are aspherical surfaces.

Values of aspherical surface coefficients of the second embodiment byEquation 1 are represented by the following Table 2.

TABLE 4 Surface Aspherical Surface Coefficient Number A B C D E F 1−0.03393 0.059682 −0.11593 0.103418 −0.03959 0 2 −0.05772 0.058269−0.10563 0.065873 −0.01574 0 3 0.019895 0.112853 −0.16386 0.118746−0.02814 0 4 0.047392 0.071129 0.128642 −0.17021 0.225302 0 5 −0.179140.061085 −0.0907 0.15285 −0.09738 0 6 −0.10604 −0.16863 0.135673 −0.0162−0.08815 −0.03569 7 −0.3988 0.478275 −1.32947 0.094656 1.84743 −1.476388 −0.02051 −0.24644 0.394981 0.069601 −0.59853 −0.15297 9 0.0362930.026184 0.001117 −0.00217 −0.00112 −0.00033 10 −0.0485 −0.005360.017149 −0.00062 −0.00185 −0.00021

Through the above-mentioned embodiments of the present invention, asshown in FIGS, 2, 3, 5, and 6, the subminiature optical system withexcellent high definition while having a small size and a relativelynarrow view angle may be obtained.

In particular, since the subminiature optical system has the relativelynarrow view angle and is configured of five lens sheets, thesubminiature optical system having high resolution and thinness may beimplemented.

In addition, since the subminiature optical system has the narrow viewangle, it may clearly capture an image of a subject at long distance.

The subminiature optical system according to the present embodiment maybe used solely in a portable device. However, in this case, it may beinconvenient to capture an image having a wide background.

Therefore, the subminiature optical system according to the presentembodiment may be employed in a portable device or the like as part of apair with an optical system having a wide view angle.

FIG. 7 is a perspective diagram schematically showing a portable deviceaccording to an embodiment of the present invention.

Referring to FIG. 7, the portable device 300 according to the presentembodiment includes a camera module 35, wherein the camera module 35 mayinclude at least two subminiature optical systems 32 and 33.

Here, the two subminiature optical systems 32 and 33 may be a firstoptical system 32 having the relatively wide view angle and a secondoptical system 33 having the relatively narrow view angle.

In addition, the first optical system 32 may be an optical system havingthe view angle between 60 degrees and 80 degrees, and the second opticalsystem 33 may be an optical system having the view angle of 35 degreesor less as described above.

As such, in the case in which one portable device 300 is provided withthe first optical system 32 and the second optical system 33, the widebackground may be imaged at the wide angle using the first opticalsystem 32, and a subject at long distance may also be clearly imagedusing the second optical system 33, as needed.

In addition, when imaging the subject, the first optical system 32 andthe second optical system 33 are simultaneously driven so as to capturetwo images at once, such that images having different focal distancesmay be simultaneously captured and a task such as an image synthesis orthe like may be performed, as needed.

As set forth above, since the subminiature optical system according tothe embodiment of the present invention only uses five sheets of lenses,the subminiature optical system having a compact shape and a shortoverall length due to a lower lens configuration number may be provided.

In addition, as set forth above, the subminiature optical systemaccording to the embodiment of the present invention may promotelightness by using the lens formed of the plastic material, may bemass-produced due to ease of fabrication, and may significantly reducemanufacturing costs.

In addition, as set forth above, the subminiature optical systemaccording to the embodiment of the present invention may have the narrowview angle of 35 degrees or less. Therefore, the subminiature opticalsystem according to the embodiment of the present invention may clearlyimage a subject at long distance.

In addition, as set forth above, the portable device according to theembodiment of the present invention may include the first optical systemhaving a relatively wide view angle and the second optical system havinga narrow view angle. Therefore, the wide background may be imaged at thewide angle using the first optical system, and the subject at the longdistance may also be clearly imaged using the second optical system, asneeded.

While the present invention has been shown and described in connectionwith the embodiments, it will be apparent to those skilled in the artthat modifications and variations can be made without departing from thespirit and scope of the invention as defined by the appended claims.

What is claimed is:
 1. An optical system, comprising: a first optical system; and a second optical system having an angle of view narrower than that of the first optical system, wherein the second optical system comprises a plurality of lenses sequentially disposed from an object side, wherein lenses disposed toward the object side are defined as a first group, and lenses disposed toward an image side are defined as a second group, based on a greatest distance on an optical axis between the lenses, wherein the first group comprises at least three plastic lenses, wherein the second group comprises at least two plastic lenses, wherein a lens, disposed farthest from the object side among the lenses of the second group, has positive refractive power, and wherein the second optical system satisfies the following conditional expression: 0.7<TTL/F<1.0 where TTL is a distance on the optical axis between an object-side surface of the lens, among the lenses, disposed closest to the object side and an image plane of an image sensor, and F is a focal length of the second optical system.
 2. The optical system of claim 1, wherein at least one lens among the at least three lenses of the first group has a positive refractive power.
 3. The optical system of claim 2, wherein the at least one lens has an object-side surface and an image-side surface, each of the object-side surface and the image-side surface is an aspherical surface, and the object-side surface is convex.
 4. The optical system of claim 1, wherein the at least two lenses of the second group comprises at least one lens having a positive refractive power and at least one lens having a negative refractive power.
 5. The optical system of claim 4, wherein the at least two lenses each have an aspherical surface.
 6. The optical system of claim 1, wherein a view angle difference between the first optical system and the second optical system is greater than 25 degrees.
 7. The optical system of claim 1, wherein the second optical system has the view angle of 20 degrees through 35 degrees.
 8. The optical system of claim 1, wherein the first optical system has the view angle of 60 degrees through 80 degrees.
 9. The optical system of claim 1, wherein the first group comprises a first lens, a second lens and a third lens, and the second group comprises a fourth lens and a fifth lens.
 10. The optical system of claim 9, wherein the second optical system satisfies the following conditional expression: −6.46<f2/(TTL/F)<−5.04 where f2 is a focal length of the second lens.
 11. The optical system of claim 9, wherein the second optical system satisfies the following conditional expression: −3.75<f4/(TTL/F)<−2.93 where f4 is a focal length of the fourth lens.
 12. The optical system of claim 9, wherein the second optical system satisfies the following conditional expression: 0.79<d45/(TTL/F)<0.86 where d45 is a distance on the optical axis from an image-side surface of the fourth lens to an object-side surface of the fifth lens.
 13. The optical system of claim 1, wherein the second optical system satisfies the following conditional expression: 1.08<Max airgap/ct1 <1.4 where Max airgap is the maximum distance, and ct1 is a thickness of a lens disposed closest to the object side.
 14. The optical system of claim 1, wherein the second optical system satisfies the following conditional expression: 0.64<OAL/F<0.7 where OAL is a distance on the optical axis between the object-side surface of the lens disposed closest to the object side and an image-side surface of a lens disposed farthest from the object side among the plurality of lenses.
 15. The optical system of claim 9, wherein the first lens has positive refractive power.
 16. The optical system of claim 9, wherein an object-side surface of the first lens is convex.
 17. The optical system of claim 9, wherein the second lens has negative refractive power.
 18. The optical system of claim 9, wherein an image-side surface of the second lens is concave.
 19. The optical system of claim 9, wherein the third lens has positive refractive power.
 20. The optical system of claim 9, wherein an object-side surface of the third lens is convex.
 21. The optical system of claim 9, wherein an image-side surface of the third lens is concave.
 22. The optical system of claim 9, wherein the fourth lens has negative refractive power.
 23. The optical system of claim 9, wherein an object-side surface of the fourth lens is concave.
 24. The optical system of claim 9, wherein an image-side surface of the fourth lens is concave.
 25. The optical system of claim 9, wherein an object-side surface of the fifth lens is concave.
 26. The optical system of claim 9, wherein an image-side surface of the fifth lens is convex. 